The present invention relates to a method of decoloring a decolorizable image forming material.
In recent years, the amount of various kinds of information has significantly increased by spread of office automation, and so the level of information output has also increased. The information output is represented by display output and hard copy output from a printer onto paper sheets. The display output, however, requires a large scale circuit board in a display unit. This brings about problems of portability and cost. Regarding the hard copy output, a large quantity of paper as a recording medium is being consumed with increase in the information output amount. Therefore, the hard copy output is expected to be a problem with respect to conservation of natural resources. In addition, recycling of paper sheets once printed by a printer or a copying machine is expensive, since much of a bleaching agent and water are required for the recycling and consumption of electric power is enormous. Under such a situation, it is considered to decrease consumption of paper substantially by using decolorizable image forming material to print information on a paper sheet, restoring a blank sheet of paper by decoloring the formed image, and reusing the paper sheet.
Heretofore, ink which can be decolored on heating has been proposed in, for example, Published Unexamined Japanese Patent Application No. 7-81236. The ink includes a color former such as a leuco dye, a developer, and a organophosphoric compound having a decoloring power.
When such image forming material is used, however, decoloring can be done insufficiently and, as a result, a paper sheet is hard to return to the blank state. For this reason, decolorizable image forming material cannot have been put into practical use.
Under such a situation, the present inventors have proceeded with development of a new image forming material and an image decoloring method. However, we have been found that it is not always easy to decolor various image forming materials prepared by combining various components with a high decoloring rate and to maintain a good decolored state.